You can dye any 100% cotton fabric with Procion MX dyes so long as the sizing or finish can be removed (with a wash of liquid dishwashing detergent). If you buy some nice quality 100% white or unbleached cotton from a fabric shop, it's most likely fine to simply put it in the soda ash solution presoak and get the dyeing process started faster.
Each type of cloth will dye a bit differently. Remember if you switch to another type of cloth, you may have to adjust your recipe. Generally, thicker fabric uses more dye powder. Also, if you love how a particular fabric dyes, buy lots! Different seasons will give you different products that are sometimes not the same. Some are similar but can produce dye results that are not the same.
What about PFD (prepared for dyeing fabric)?
I have had good results with PFD fabrics as well as I'm often happy with any white or unbleached 100% cotton fabric intended for quilt making.
Find the fabric that has the surface and weave that works for your end projects. I use coarser weaves for those projects that will not get harder wear and firmer weaves for those fabrics that are really going to be used and washed more frequently such as children’s clothing so it holds up better with the harder wear demands.
I like to have a variety of tone on tone designs, stripes, floral patterns so the fabrics are shades of white. It is always interesting what the dye shading will be on those tone on tone fabrics and I enjoy the surprise.
Some of the companies that sell the dyes also have fabrics they recommend so that is another place to look for your fabric choices. Different weights can add variety to your finished dye projects. A pant weight and a top weight dyed with the same color can make a nice outfit.